Modern vehicles are usually equipped with an electronic stability program (ESP), which executes wheel-specific braking interventions in critical driving situations, such as when the vehicle oversteers or understeers.
In addition, conventional so-called comfort or also value-added functionalities assist the driver in a braking operation. Conventional added-value functionalities are, for example, a hydraulic brake assistant (HBA), which automatically generates brake pressure in collision-critical driving situations; an assistant in fading situations (HFC), which supports the driver when fading occurs; or an assistant for aiding the brake booster (HBB), which generates additional brake pressure in the event that the boost by the brake booster is insufficient.
To allow the implementation of such brake functionalities, the vehicles are equipped with a specially adapted brake system as it is shown in FIG. 1 by way of example. FIG. 1 shows a conventional hydraulic brake system 17, which has two brake circuits 19a, 19b in an X- or II-distribution featuring a symmetrical configuration. Below, reference is therefore made only to part 19a shown on the left side in the figure.
The brake system includes a foot brake pedal 1, a brake booster 2 having a master brake cylinder 4 connected thereto, on which a brake fluid reservoir 3 is situated. When foot brake pedal 1 is operated, corresponding pressure is built up in master brake lines 5a, 5b, this pressure acting on brakes 11 of the wheels via a switchover valve 8a and the two intake valves 10a, 10b. The path in which pressure builds up when foot brake pedal 1 is operated is indicated by arrows b. A high-pressure switching valve 7a is closed in this state (as illustrated).
In an intervention of an automatic brake functionality, the brake pressure is generated automatically, with the aid of a hydraulic pump 9a, 9b, which is actuated by a control unit (not shown). In the brake system illustrated, three pumps 9a, 9b are switched in parallel in each brake circuit. Switchover valve 8a is closed during the pressure regulation, and high-pressure switching valve 7a is usually open. Hydraulic pump 9a then conducts the hydraulic fluid to wheel brakes 11, along paths a. Thus, the hydraulic fluid flows out of brake fluid reservoir 3 through master brake line 5a, high-pressure switching valve 7a, a suction line 6a, through hydraulic pump 9a, and further through intake valves 10a, 10b, to wheel brakes 11. Brief peaks in the volume flow may be “buffered” in a compensation reservoir 14a, 14b. 
Conventional brake functionalities do indeed improve the driving safety significantly, but they also entail a few disadvantages in terms of braking comfort. As soon as an automatic braking functionality, such as HFC or HBB, is triggered, high-pressure switching valve 7a switches from the closed state to the open state. However, in this situation the driver has already generated relatively high brake pressure in master brake lines 5a, 5b at brake pedal 1, whereas very low pressure prevails in suction line 6a on the other side of high-pressure switching valve 7a. If high-pressure switching valve 7a then switches to the open state, a so-called pressure equalization knock occurs, which manifests itself as a sudden loud noise to the driver. In addition, brake pedal 1 drops by a few centimeters, which likewise is unfamiliar to the driver.